As a parallel$-$plate capacitor with circular plates $26$ cm in diameter is being charged, the current density of the displacement current in the region between the plates is uniform and has a magnitude of $23\frac{A}{m^2}.($a$)$ Calculate the magnitude $B$ of the magnetic field at a distance $r=90mm$ from the axis of symmetry of this region. $($b$)$ Calculate $d\frac{E}{d}t$ in this region.

$($a$)$ Number

Units

$($b$)$ Number $$ Units